5.7 Engine Misfire (P0300)

[Ryan Krizan]

Hello,

I have a 2000 Tahoe z71 classic (2000 model year, 1999 body style) that I'm having a misfire issue on. It started as a P0303 code, now it's the random p0300. The issue isn't constant, but seems to be more pronounced if I'm going uphill and I'm light on the throttle I'll get a vibration, followed by the check engine light. If I let off the throttle for a few seconds, and get back on it, the misfiring usually stops for a bit.

The cap, rotor, plugs and wires have been replaced. I did have a vacuum leak that I found and fixed, no change. I have my suspicions that it could either be a coil, intake gaskets, or even the CSFI spider giving me issues.

I figured I would come here and ask, to see if there is something else I should be looking at before digging in deep.

Is there another issue that could be causing the misfire? Fuel pressure is good. Engine runs great when ******* the throttle. Any insight would be greatly appreciated!

 

[iamdub]

Check the tip of the crankshaft position sensor to see if it has any marks on it from contact with the reluctor wheel. Even if it hasn't contacted, it could still misread under load if there's less than .030" clearance. You can measure it or just add a shim or two just to try it out.

Shim kit:

https://www.eficonnection.com/home/product/sensor-shim-kit

If the sensor is damaged, it should be replaced. A CKP relearn should be performed even if it appears to be operating as normal after sensor replacement or after the shim(s) is/are added.

 

[rockola1971]

I had a 99 GMC Sierra with a 5.7l (just sold it 3 weeks ago). It notoriusly needed a cap and rotor atleast once a year. The Vin R 5.7l are notorious for intake manifold gasket leaks. Could also be a spider leg going to an injector which are notorious for cracking (spider leg). You need to get a better clue if this detonation problem is ignition related OR fuel delivery related. Run a scan and see if you are running lean or rich during the condition (load it down and watch). Lean means you are fuel starved and rich means it aint burning correctly (ignition).